1. Field of the Invention
The present invention relates generally to methods and apparatus for percutaneous surgery and, more specifically, to a method and apparatus for performing percutaneous transforaminal lumbar and thoracic disc surgery and interbody fusion.
2. Description of Prior Art
A substantial segment of the population suffers from spinal pain that is caused by degenerative, herniated or protruded intervertebral discs. Intervertebral discs are members of the spinal column that serve as cushions and mobile linkage elements between the individual vertebrae. The acute herniation of an intervertebral disc can lead to the compression of spinal nerve elements within the spinal canal as well as disc surfaces outside of the spinal canal. The problem can cause severe back pain, leg pain, muscle weakness, and possibly bowel and bladder dysfunction.
The traditional surgical method of spinal nerve element decompression is by the transcanal methods of laminectomy or laminotomy. Optical aids such as microscopes, endoscopes or loupes are often used in these processes. The tissue retractor commonly used in this type of surgery is normally constructed with two blades. More recently, a tubular shaped retractor has been used. Traditionally, this procedure has required two to three days of hospitalization after completion of the surgery.
Chronic back pain due to disc failure, without dominant extremity symptoms may also cause chronic functional impairment. Prior art solutions have surgically fused adjacent vertebrae together by placing bridging bone material from one vertebra above to one vertebrae below the symptomatic disc(s). The bone fusion surfaces may include the posterior vertebral elements, the vertebral end plates or a combination of the two. Sometimes, metal rods and screws have been used to stabilize the subject spinal fusion segment from the posterior approach.
Because of the tremendously invasive nature of many prior art techniques as compared to the present invention, these prior art techniques caused significant access tissue trauma, even when the skin incision was reduced in length.
Using endoscopic transforaminal techniques, a surgeon can operate through a smaller (roughly 8-12 millimeters) opening with endoscopic surgical viewing instruments and miniaturized tools.
The preferred method using endoscopic techniques and miniaturized instrumentation results in an even less intrusive procedure. Because the access surgical trauma and destabilization are less with this technique, endoscopic transforaminal surgery requires a shorter rehabilitation time.
The preferred technique of the present invention adopts an extraspinal canal approach for the correction of spinal conditions, herniated discs and chronic disc pain. In using this approach, the perils of nerve element and dural from sharp trauma and retraction trauma are greatly reduced. The working channel for simple herniated disc extraction is approximately 8 mm in diameter and the diameter is somewhat larger for fusion surgery. Because of the ultra miniaturization of the instruments, the procedure can be performed using local anesthetic agents and conscious sedation. Unlike prior art, overnight hospital stays are not necessary.
In an alternative methodology, the body is opened up as much as necessary. The remaining portion of the access to the target site is conducted using the minimally invasive techniques and tools as described herein. This surgical technique is less invasive than prior art, but more invasive than the preferred methodology of this invention.
To fuse adjacent vertebrae, bone graft material is placed in the evacuated disc space between the bony end-plate of the target vertebrae. After insertion of the structural bone graft material and any additional non-structural osteogenic agents, ingrowth of new autologous bone gradually replaces the graft material to create a unified structure that includes the first and last vertebrae in the fusion segment. Prior art techniques have used structural angular bone blocks, metallic cages, carbon fiber blocks or bone chips that are inserted into the intervertebral space(s). Prior art laparoscopic anterior lumbar fusion technique uses cylindrical metallic cages or bone dowels. These cylindrical shaped devices do not achieve maximum surface contact with the flat surface of the host end plate bed. Thus, seating of cylindrical/round shaped fillers requires end-plate cutting. Surgical end-plate cutting structurally weakens the end-plate and introduces the probability of metallic fillers settling into the soft vertebral cancellous body. In contrast, the preferred mode of the present invention uses modular discoid shaped fillers that do not need end-plate cutting for seating and stability.
However, prior art lateral approached spinal, square shaped graft delivery tubes are bulky. The dimensions of block graft delivery via a prior art square tube can not take full advantage of the maximum outer dimensions of the delivery tube. Additionally, these prior art systems have no method for graft insertions into the L5-S1 disc space. Because prior art minimally invasive systems require generally round tube delivery conduit, the subsequent graft shape is necessarily round/cylindrical as well.
One specific prior art technique, using a rounded filler, is discussed in U.S. Pat. No. 6,217,509 (the '509 patent). The '509 patent describes an access tubular channel from the skin to the targeted work area (which is only used in the posterior transcanal spinal approaches). The working channel inside the tube allows for the use, as needed, of a viewing element, operating tools, tissue retractors, suction channels and a fluid channel. This method is considered more problematic when used in any other approach. According to the '509 patent, a fluid working environment is not desirable in posterior lumbar surgery. However, a fluid environment is utilized in the present invention without degrading endoscopic vision during the ablation of bone, collagenous tissue or bleeder coagulation. A Holmium-YAG laser, used in a fluid medium, in the present invention, eliminates the problems that encountered by the '509 method.
Additionally, the '509 patent does not identify the necessary skin entry location for instruments insertion nor the safe portal into the vertebral annulus. The present invention describes a skin window localization method, identified the safe foraminal annular window and the trajectory for the instruments. In sequential steps the working cannula, viewing element and all other operating tools enter the same windows. In addition, the deep end of the duty cannula is anchored in the opening of the annular window.
Finally, the '509 method neither describes nor allows for the delivery of modular discoid shaped bone graft material (i.e., components of the module are rectangular or have round edges that face the interior of annulus fibrosus).
Therefore, a surgical method, preferred shaped tool(s) and preferred shaped conduits are needed that allow modular discoid shaped filler components, of variable shape and size, to be implanted into an intervertebral disc space using percutaneous endoscopic transforaminal spinal surgery methodology.